Engines may include crankcase ventilation systems to vent gases out of the crankcase and into an engine intake manifold to evacuate gases from inside the crankcase in order to reduce degradation of various engine components in the crankcase. The crankcase ventilation systems may include a positive crankcase ventilation (PCV) valve for enabling one-way flow of crankcase gases from inside the crankcase to the intake manifold.
Crankcase ventilation systems are intermittently diagnosed for PCV valve degradation. One example approach for PCV valve diagnostics is shown by Rollinger in US 2014/0081549. Therein, PCV system diagnostics are implemented using a pressure sensor coupled to a hose extending between an intake conduit upstream of a compressor and an oil separator in the crankcase. A pressure drop indicated by the pressure sensor during unboosted conditions is used to ascertain a PCV system breach. It will also be understood that traditional PCV systems are disabled during boosted conditions in engines with turbochargers, superchargers, etc., due to the positive pressure present in the intake manifold.
The inventors herein have recognized potential issues with such approaches. As one example, no diagnostic method is provided during boosted conditions in Rollinger's system. As such, the PCV system may only be diagnosed during a limited window of engine operation. This problem is exacerbated in boosted engines with a low power to weight ratio, where boosting occurs over a wide range of engine operating conditions. Furthermore, in Rollinger the PCV system is not designed to vent crankcase gasses during boosted conditions. As such, the crankcase may experience elevated pressures and degradation due to oil dilution, seal leaks, and other problems associated with crankcase gas contamination caused by blow-by gasses. More generally, some PCV systems have suffered from unreliable diagnostic routines which may lead to false positives.
In one approach, to at least partially address these issues, a PCV system diagnostic method is provided. The method includes while intake manifold air pressure is above a threshold boost value, a determination of a PCV system breach is made and is based on a pressure measured by a pressure sensor positioned in the PCV system. The sensor is positioned on a clean side of an oil separator coupled to the crankcase. The PCV fresh air ventilation line provides fluidic communication between the oil separator and the intake conduit upstream of a compressor. In this way, a diagnostic method may be implemented while the PCV system vents crankcase gas during boosted engine operation. As a result, the PCV system may be diagnosed over a wider range of engine operating conditions, making the engine's overall PCV diagnostic routine more robust. Furthermore, the likelihood of crankcase degradation caused by gas contamination from blow-by gasses, elevated crankcase pressures, etc., is driven down.
In one example, the PCV breach may indicate the ventilation line is leaking and/or disconnected from the oil separator and/or the intake conduit. In this way, specific regions of the PCV system can be accurately diagnosed, allowing mitigating actions tailored for selected areas of the PCV system to be taken, if desired.
In another example, responsive to determining the PCV system breach, boost provided to the engine via the compressor is adjusted based on the pressure sensor pressure, for example, to moderate the impacts of a breached ventilation line.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.